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The origin of life

Tree of life

How did life begin?

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How did life appear on Earth?

Tree of life

How did life begin?

Why it was not even a question for most of the human being’s time.

• Some version of “the gods did it”

• Vitalism

• Spontaneous generation

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Spontaneous generation

How did life begin?

•The beginning of life forms from inanimate objects has been accepted for centuries

•In ancient Egypt it was believed that the heat of the Sun on the sediments of the Nile produced snakes and crocodiles

•In Middle Ages people accepted without any questioning that mud, mist, sunlight and air could become frogs, insects, rats and every type of inferior plant, fungi or animal.

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Spontaneous generation

How did life begin?

Lamb of Tartary. Most people used to believe that animals could grow from plants

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Spontaneous generation

How did life begin?

• Even in 1667 Jan Baptist van Helmont, a Flemish doctor, wrote a recipe to produce mice: it was required the sweaty underwear of a woman and a handful of wheat grains into a barrel. “After 21 days the smell changes and penetrates the wheat grains, turning the wheat into mice”

• In 1668 the Italian doctor Francesco Redi showed how the maggots in the rotting meat came from flies’ eggs

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Spontaneous generation

How did life begin?

• In fact spontaneous generation was not fully questioned until the experiments of the French chemist Louis Pasteur in the second half of the ninetieth century.

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Spontaneous generation does not occur

How did life begin?

• Nowadays it is recognized beyond any doubt that existing living beings come from pre-existing living beings

and that life forms –no matter how simple– cannot be originated from decaying or decomposing of matter.

• But then… how did the first living beings come to existence?

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Something happened in between

How did life begin?

This is the aspect of the Earth 4000 million years ago. The impacts were so violent and so continuous that the crust was totally burning liquid lava.

This is one of the oldest rocks we can find on Earth. It was formed 3500 million years ago. The parallel lines are fossils of cyanobacteria.

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The first living beings

How did life begin?

These wavey patterns could be 3.700 million-year-old fossils. They were discovered in August 2016.

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Today stromatolites

How did life begin?

These round formations are stromatolites. In swallow waters the cyanobacteria grow in layers and produce a typical pattern of deposits of CaCO3 .

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The first living beings

How did life begin?

Since the 19th Century, biologists have known that all living things are made of "cells": tiny bags of living matter that come in different shapes and sizes. Cells were first discovered in the 17th Century, when the first modern microscopes were invented, but it took well over a century for anyone to realize that they were the basis of all life.

1213/02/17

The first living beings

How did life begin?

In April 2016, scientists presented an updated version of the "tree of life": a kind of family tree for every living species. Almost all of the branches are bacteria. What's more, the shape of the tree suggests that a bacterium was the common ancestor of all life. In other words, every living thing – including you – is ultimately descended from a bacterium.

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The first living beings

How did life begin?

This means we can define the problem of the origin of life more precisely. Using only the materials and conditions found on the Earth over 3.5 billion years ago, we have to make a cell.

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But hold on for a moment, please

How did life begin?

We have just said that “Using only the materials and conditions found on the Earth over 3.5 billion years ago, we have to make a cell.”And what if life did not begin on the Earth? What if life came from outside in the space?

1513/02/17

Panspermia!!

How did life begin?

In 1903 the Swedish chemist Svante Arrhenius made popular the idea that life could have come to the Earth from somewhere out in space. Comets and meteorites could have done the job. Did he have a proof? Not a single one.

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Panspermia!!

How did life begin?

It seems difficult to take seriously such idea and panspermia has been long forgotten until… Evidences are suddenly falling from the skies!!!

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Evidences of Panspermia

How did life begin?

•The interstellar dust is mostly made of large organic molecules• Many different bacteria have been discovered above 41 km in the atmosphere• Streptococcus mitis in Surveyor 3 survived 3 years in the surface of the moon

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Evidences of Panspermia

How did life begin?

•Lichens and even tardigrades have resisted the space conditions out the ISS• There could be fossils in ALH84001• Uracil and xanthin in the Murchison meteorite

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Types of Panspermia

How did life begin?

• Radiopanspermia refers to single spores or seeds driven by the radiation pressure from stars• Lithopanspermia refers to spores or cells carried inside comets or meteorites• Molecular panspermia or pseudopanspermia refers to the traveling of organic molecules instead of cells or spores• Directed panspermia concerns the deliberate transport of microorganisms in space, sent to Earth to start life here, or sent from Earth to seed new planeary systems with life

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Supporters of Panspermia

How did life begin?

• Does it sound like crazy to you?• Here you have a list of some scientist in favor of panspermia:

– Fred Hoyle– Francis Crick– Stephen Hawkins– Svante Arrhenius

• It’s not only that all of them won the Nobel prize in their specific areas, but that they have proved to be right in the past when they prophesize events to occur

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The panspermia inconvenient

How did life begin?

Even if the supporters of panspermia are right, and life began on Earth as a consequence of spores, cells or seeds form outer space this does not solve the mystery of the origin of life because if life came from outside how did it started in the first place?

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An old (and wrong) idea: Vitalism

How did life begin?

Before 1800s most people believed in vitalism. It is the intuitive idea that living things were endowed with a special, magical, property that made them different from inanimate objects.

The Bible says that God used “the breath of life” to animate the first humans. And the immortal soul is a form of vitalism.

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A wrong idea: Vitalism

How did life begin?

In the XIX century chemists showed how living things were not made of special materials or special types of energy.

Despite of that, scientists were still reluctant to look for a deity-free explanation of life. Perhaps they were still too emotionally attached to vitalism.

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Always ahead of times: Darwin

How did life begin?

In 1859 Charles Darwin showed how all the present living beings were all descendants of a primordial organism that lived millions of years ago: the last universal common ancestor.Darwin and his idea came under a ferocious attack because it contradicted the Bible.Darwin did not dare to write in his book where this first organism came from.

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Always ahead of times: Darwin

How did life begin?

Darwin knew that it was a profound question, but – perhaps wary of starting yet another fight with the Church – he only seems to have discussed the issue in a letter written in 1871. His excitable language reveals that he knew the deep significance of the question:

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Always ahead of times: Darwin

How did life begin?

"But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes..."

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Abiogenesis: the primeval soup

How did life begin?

In 1924, Alexander Ivanovich Oparin published his book The Origin of Life. In it he set out a vision for the birth of life that was startlingly similar to Darwin's warm little pond.

4000 mya the crust was a mess of semi-molten rocks with constant volcanic activity. The gases of the volcanoes formed the ancient atmosphere and they reacted due to the energy of storms and solar radiation. Simple organic molecules were formed.

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Abiogenesis: the primeval soup

How did life begin?

According to Oparin, as the Earth cooled down intense continuous rain produced the primitive seas and organic molecules accumulated on them (he called them “primordial soup”).

Some chemicals would react with others to produce more complex compounds. Oparin thought that molecules central to life would have appeared in the water.

But some organic chemicals do not dissolve in water and form spherical globules in aquatic environments .

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Abiogenesis: the primeval soup

How did life begin?

Some of the spherical globules would have incorporated inside the complex organic molecules that would have continue with the chemical reactions. Oparin called this globules “coacervates”.

Coacervates can take substances from the surrounding water and also they can divide.

Oparin proposed that coacervates were the ancestors of the first real cells that he called “protobionts”.

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Abiogenesis: the primeval soup

How did life begin?

In 1929, the English biologist J. B. S. Haldane independently proposed some very similar ideas than those of Oparin.

Just like Oparin, Haldane outlined how organic chemicals could build up in water, "[until] the primitive oceans reached the consistency of hot dilute soup". This set the stage for "the first living or half-living things" to form, and for each one to become enclosed in "an oily film".

The idea that life formed in a primordial soup of organic chemicals became known as the Oparin-Haldane hypothesis.

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Abiogenesis: Miller’s experiment

How did life begin?

In the earliest 1950s Harold Urey was giving a lecture on the Oparin-Haldane hypothesis. He stated that, more than probably, there wouldn’t be oxygen in the primeval atmosphere.

In the audience a young student, Stanley Miller, asked the professor and Nobel prize if someone had tried to show the abiogenesis processes in the laboratory.

Urey, a renowned chemist that had worked in the Manhattan Project and an activist for the civilian control of nuclear energy, got impressed.

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Abiogenesis: Miller’s experiment

How did life begin?

So, in1952 Stanley Miller began the most famous experiment on the origin of life ever attempted.

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Importance of Miller’s experiment

How did life begin?

In only on week, Miller obtained several amino acids and other bio-molecules very important for living cells. The results were published in Science in 1953.

It showed that it is possible, and easy, to obtain the building blocks of life from simple and abundant substances that could be present in the primeval atmosphere in the conditions supposed for the Earth of 4000 millions years ago.

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Life is more complicated

How did life begin?

This very same year, 1953, in Nature, Watson y Crick published the DNA structure.

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Differences of approach

How did life begin?

Suddenly the origin of life attracted a lot of interest from many different scientists. They began to work on very different fields depending on their favorite characteristic of life.

Genetics firstThey focus on the ability of the cells to dividide passing information to their descendants.

Metabolism firstCells need to use a source of energy to perform the vital functions.

Compartmentalisation first Cells are separate from the environment by biological membranes.

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Genetics first

How did life begin?

The first living beings had to do copies of themselves for the ability of replication seems to be central for life.

This first replicator would probably be RNA because it has been found that some RNA molecules can also catalyze chemical reactions working as “ribozymes”.

In 1986 Walter Gilbert proposed that life began in the "RNA World".

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Genetics first

How did life begin?

But no self-replicating RNA had been found, and nobody could figure out how RNA formed in the primordial soup. This is the reason why other replicators have been proposed:

• Polyamide Nucleic Acid, or PNA: In 2000 Miller repeated his famous experiment and obtained the polyamide backbone of PNA.

• Threose Nucleic Acid, or TNA: 2000.

• Glycol Nucleic Acid, or GNA: 2005.

The alternative nucleic acids might solve the latter problem, but there was no evidence they ever existed in nature.

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Metabolism first

How did life begin?

Before an organism can reproduce, it has to be self-sustaining. It must keep itself alive. After all, you cannot have kids if you die first.

First, you must obtain energy; say, from energy-rich chemicals like sugars. Then you must use that energy to build useful things like cells.

This process of harnessing energy is so utterly essential, many researchers believe it must have been the first thing life ever did.

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Metabolism first

How did life begin?

Life would be an organized set of chemical reactions and minerals would provide the materials and the catalytic power to catch and use the energy required for self-organization.

The ideal place for the beginning of life would be the hydrothermal vents at the bottom of the oceans. The rocks of alkaline vents were porous: they were pocked with tiny holes filled with water. These little pockets would act as "cells". Each pocket contains essential chemicals, including minerals like pyrite. Combined with the natural proton gradient from the vent, they were the ideal place for metabolism to begin.

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Compartmentalisation first

How did life begin?

Reproduction or metabolism cannot take place in abstract. First, a container is required to keep all the essentials of life together.

Any fatty or oily substance will form blobs or films in water. These chemicals are collectively known as lipids, and the idea that they formed the first life has been called the "Lipid World".

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The “everything first” hypothesis

How did life begin?

In 2001, Szostak and Luisi, writing in Nature, argued that it should be possible to make simple living cells from scratch, by hosting replicating RNAs in a simple, fatty blob.

Three years later they found out that using montmorillonite, a type of clay, the blobs formed hundred of times faster and they could absorb RNA molecules.

The “everything first” hypothesis brings a radical new idea about the origin of life, namely that all the key components of life could be formed at once.

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The “everything first” hypothesis

How did life begin?

John Sutherland imagines small rivers and streams trickling down the slopes of an impact crater, leaching cyanide-based chemicals from the rocks while ultraviolet radiation pours down from above. Each stream would have a slightly different mix of chemicals, so different reactions would happen and a whole host of organic chemicals would be produced.

Finally the streams would flow into a volcanic pond at the bottom of the crater. It could have been in a pond like this that all the pieces came together and the first protocells formed.

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The "Hodge-Podge World"

How did life begin?

That means we are approaching one of the great divides in human history: the divide between those who know the story of life's beginning, and those who never could.

Some of the people alive today will become the first in history who can honestly say they know where they came from. They will know what their ultimate ancestor was like and where it lived.

This knowledge will change us. On a purely scientific level, it will tell us about how likely life is to form in the Universe, and where to look for it. And it will tell us something about life's essential nature. But beyond that, we cannot yet know the wisdom the origin of life will reveal.